1. Field of the Invention
Embodiments of the present invention relate to a semiconductor device.
2. Description of the Related Art
Semiconductor devices such as power diodes and insulated gate bipolar transistors (IGBTs) are provided in power converting equipment such as converters and inverters and are indispensable for controlling rotary motors and servomotors.
FIG. 12 is a plan diagram depicting an overall view of a semiconductor device 600 having a conventional trench structure. FIG. 13 is a cross-sectional view of the semiconductor device 600 along cutting line XIII-XIII in FIG. 12. An IGBT is taken as an example for the semiconductor device 600.
In FIGS. 12 and 13, an n buffer layer 62 is disposed on a p collector layer 61 disposed in a semiconductor substrate 83, and an n drift layer 63 is disposed on the n buffer layer 62. A p well layer 64 is disposed in the surface layer of the n drift layer 63. A trench 65 is disposed that penetrates the p well layer 64 and that reaches the n drift layer 63. The trench 65 is filled with a polysilicon to dispose a gate electrode 68 via a gate insulating film 67 on an inner wall. An n emitter layer 70 is selectively disposed in a surface layer of the p well layer 64 between the trenches 65.
An IGBT cell 72a includes the p collector layer 61, the n buffer layer 62, the n drift layer 63, the p well layer 64, the n emitter layer 70, and the gate electrode 68 disposed in the trench 65. The p collector layer 61 is connected to a collector electrode 84 and the n emitter layer 70 is connected to an emitter electrode 85. The emitter electrode 85 and the gate electrode 68 are electrically isolated from each other by an interlayer insulating film 82. An IGBT cell group 72 to be an aggregate of the IGBT cells 72a is divided by a gate runner 74 into four and is disposed in an active region 86. The gate runner 74 is connected to a gate terminal 88.
FIG. 14 is an equivalent internal circuit diagram of the semiconductor device 600 depicted in FIG. 12. The plural IGBT cells 72a are connected to each other in parallel, and the gate runner 74 is connected to the gate terminal 88. The collector electrode 84 of the IGBT cell group 72 is connected to a collector terminal 89 and the emitter electrode 85 of the IGBT cell group 72 is connected to an emitter terminal 90.
When an ON signal is input to the gate terminal 88, each of the IGBT cells 72a is simultaneously turned on. Reduced cell intervals consequent to advancements in fine fabrication and high performance IGBTs (the semiconductor device 600), which include many cells, have increased electron injection efficiency to enable greater collector current to flow with the same chip size (the size of the semiconductor substrate 83). Therefore, the di/dt, which is the instantaneous rate of change in current over time, becomes large with turning on and turning off events.
When the di/dt becomes great, vibration is caused in the current and the voltage at turning on and turning off events. The vibration of the current and the voltage generate radiation noise resulting in the inconvenience of malfunctions of an adjacent gate driving circuit and an adjacent electronic device in addition to malfunctions of the IGBT itself.
An IGBT has been proposed that includes plural independent gate terminals and gate driving circuit that includes a shift resistor, where gate output signals are sequentially delayed and input to the gate terminals to prevent vibrations (for example, refer to Japanese Laid-Open Patent Publication No. H8-32064). As a result, the cells of the IGBT cell group are sequentially delayed to be turned on or turned off whereby the di/dt becomes gradual.
With the method described in Japanese Laid-Open Patent Publication No. H8-32064, a shift resistor circuit is necessary and a problem arises in that the driving circuit becomes complicated.